For some questions you can immediately cancel down to a fraction out of 100, and this gives you the percentage. For instance, cancels down by a factor of two to make so equals 71%. Alternatively you might cancel a fraction down to one you have memorised from the list above, e.g. simplifies by a factor of two to make which is 62.5% — many mental questions involve the eighths so it is best to learn their percentage conversions by heart!

Other times you need to build a fraction up, for instance becomes or 26% when you multiply numerator and denominator by two. You might also need a combination of these methods, for example cancels down by a factor of three to make , which can then be built up to or 36% by multiplying numerator and denominator by four.